Odors emanating directly from manure or produced during its anaerobic digestion can create conflicts at the urban-rural interface. This may motivate pig and other domestic animal farm operations to relocate or reduce production as a means of limiting the odor problem. Both of these responses negatively impact agricultural economic interests. Similarly, domestic animals, such as dogs and cats, create malodor problems in their owner's home. Indeed, odors from human fecal waste in portable facilities and traditional outhouses can be prohibitive.
Persaud et al. reports that manure, fecal, and urine odors consist of volatile, odorous, organic acids as well as fecal-smelling sulfur compounds and indoles. Persaud et al., in Chem. Senses, 21:495–505, June, 1996. Persaud et al, however, does not disclose or suggest odor-reducing methods.
Agents previously used in odor reduction include compounds that have been approved and used for reduction of fecal malodor in human patients and reduction of malodor and off-flavors in human drinking water. Both bismuth compounds as well as chlorophyllin copper complex (CCC) have been approved by the Food and Drug Administration (FDA) for “internal deodorization” of human ostomy- and colostomy-related odors. Federal Register, final monograph 55 (#92) “19862–19865. Powdered activated charcoal (PAC) is routinely used by water utilities to remove unfavorable flavors and odors from potable drinking water. Suffet et al., Amer. Water Works Assoc. Res. Found., 157–208, 1995. These substances act in several ways to reduce and/or eliminate odors. Pierce et al., Chem. Senses, 20: 401–411, 1995.
Chlorophyll is the major photo-synthetic porphyrin pigment in plants. Both it and several chemical derivatives appear to exhibit interesting biological activities. CCC is one of the derivatives of plant chlorophyll. Chernomorsky et al., N. J. Medicine, 85: 669–673, 1988, reports that CCC exhibited deodorizing properties when applied to foul smelling wounds and that CCC may be effective in controlling the odor problems of ostomy/colostomy patients.
Others report that the deep insertion of chlorophyll derivatives by patients into their colostomy bags led to significant deodorization. Golden et al., Gastroenterol., 31: 260–265, 1956; Siegel, Gastroenterol., 38: 634–636, 1960. These papers also report that oral administration of CCC to colostomy patients in doses of 100–200 mg daily was sufficient to control malodors without undesirable side effects. Chernomorsky et al. reports that dosages up to 800 mg/day have been safely used. Studies in which 100–200 mg doses of CCC were administered to patients with urinary and fecal incontinence problems resulted in a marked reduction in malodor after the first week of treatment. Young et al., J. Amer. Geriatrics Soc., 28: 46–47, 1980; Doty, Nursing Homes, 20–28, 1971.
Although the exact mechanisms by which chlorophyll derivatives, such as CCC, promote deodorization are not fully understood, several hypotheses have been presented. First, chlorophyll exhibits antimicrobial effects upon microbes that produce malodorous materials (anaerobes). Second, the molecular structure of the molecule makes it able to interact with a variety of odorous materials that have free, lone pairs of electrons which may form inter-molecular (albeit not covalent) bonds with chlorophyll derivatives. As a result, chlorophyll derivatives have been found to bind tightly and immobilize odorous indole-like compounds produced by microbes. Third, chlorophyll derivatives may induce metabolic changes in odor-causing bacteria by altering certain enzymes or binding enzymes in these bacteria, thereby altering metabolic pathways with a subsequent diminution of odoriferous metabolites. Finally, the metal ion within CCC may act as the lone agent to influence and alter metabolism of bacteria. Copper may react directly with malodorous compounds such as volatile sulfur compounds to produce copper sulfides and take them out of the vapor phase, rendering any mixture that contains these compounds less odorous.
In addition to CCC, bismuth compounds have been shown effective in reducing fecal odor. Historically, bismuth compounds have been used to ameliorate gastrointestinal disorders. Modem studies have shown that relief comes as a result of these compounds acting on the gastrointestinal microflora. Cormick et al., Reviews of Inf. Diseases, 12 Suppl 1: S9–10, 1990; Sox et al., Amer. Soc. for Microbio., 33: 2075–2082, 1989. Bismuth and its salts are toxic to many forms of microflora and can be used to treat many digestive disorders, including ulcers caused by the bacteria Helicobactor pylori. Goh et al., Gastroenterol., 26: 1123–31, 1991; Blaser, Scientific Amer., 104–107, Feb, 1996.
The bismuth compounds have also been used as part of treatments for reduction of malodor from fecal material. Bismuth subgallate (BiG) has been approved by the FDA for “internal deodorization” of ostomy and colostomy related odors. Federal Register, final monograph 55 (#92) “19862–19865. As reported therein, BiG pills can be taken orally and/or added to ostomy/colostomy bags.
The bismuth compounds act in two ways, either by reducing the number of odor-producing anaerobic intestinal microbes or by directly interacting with sulfur containing compounds which are thought to be the primary malodor producing volatiles. Chernomorsky et al., N.J. Medicine, 85: 669–673, Aug. 1988. Bismuth compounds may also interact with organic acids to form organic acid bismuth salts, further inhibiting their volatility and, as a result, inhibiting their ability to be odoriferous.
PAC has been used by water utilities to absorb odorants and tastants from an aqueous environment via vigorous mixing. PAC provides a large surface area on which odorous organic compounds can be absorbed and retained. Although PAC, in various particle sizes, has also been used as a sorbent by chemists and physicians, its potential use as an odor absorber in other applications has not been examined.
Previous use of powdered carbon proved ineffective at reducing swine slurry odor. Warburton et al., 1980 Proceeding of the Fourth International Symposium on Livestock Wastes, p. 309–313. However, PAC can provide considerable odor reduction of swine slurry when used alone or in combination with other agents described above.
Olfactory cross-adaptation (“cross-adaptation”) is another methodology for inhibiting the perception of malodor. Cross-adaptation is the decrease in the perceived odor sensitivity to one odorant after exposure to another odorant. Cross-adaptation has commonly been interpreted as a measure of the degree to which odors share common sensory channels. Although it has long been known that perceptual similarity influences cross-adaptation, recent evidence suggests that structural similarity, in the absence of perceptual similarity, can also influence cross-adaptation. Pierce et al., Chem. Senses, 20: 401–411 (1995); Pierce et al., J. Soc. Cosmet. Chem., 47: 363–375 (Dec. 1996). Pierce et al. report the cross-adaptation of sweaty-smelling 3-methyl-2-hexenoic acid (3M2H) by its ethyl esters.
There remains a need for compositions and methods for reducing malodor from animal urine and fecal matter in, inter alia, farming operations, the home, and in human, stand-alone facilities.